The present invention relates generally to semiconductor crystal growth, and, in particular, relates to a device used in an apparatus for crystal growth at high temperatures and pressures.
In order to grow semiconductor crystals of very high quality, a furnace must provide a highly defined temperature gradient that may be adjusted in a desired manner. A heat pipe used in a furnace is disclosed in U.S. Pat. No. 3,677,329. This prior heat pipe includes concentric inner and outer cylindrical metal tubes. The space between the tubes forms an annular chamber (the cavity within the inner tube forms a working space). The surfaces of the tubes disposed within the annular chamber are covered with linings of porous wick material. The two wick linings are spaced apart and joined together by short spacer elements of wick material that are spaced along the length of the tubes. The annular chamber is closed at both ends by annular shaped cover plates which leave the isothermal working space open for easy access from the outside. The annular chamber is evacuated of non-condensable gases, such as air, and contains a vaporizable fluid of sufficient quantity to wet the entire wick material by capillary action. The specific fluid depends upon the operating temperature desired for the heat pipe.
The wick material for the linings and spacer elements may be in the form of sintered metal wire screens, or other porous compacts having voids or openings of capillary size and capable of transporting the vaporizable fluid.
The working space being devoid of working fluid can be used in a furnace to process various articles of manufacture such as semiconductive devices without danger of contamination by the working fluid. In addition, the furnace may be used to provide an isothermal environment for various components requiring uniform thermal distribution with the furnace shaped in conformity therewith.
A metal casting apparatus for making single crystals is described in U.S. Pat. No. 3,770,047. This apparatus has a first annular heat pipe, arranged along a longitudinal axis, and is provided with a heater means such as RF coils for establishing within the first heat pipe a first uniform temperature above the liquidus temperature for the alloy to be cast. A second annular heat pipe is arranged end-to-end with the first one and with means for establishing within the second heat pipe a lower uniform temperature below the solidus temperature of the alloy.
A mold is placed within the first higher temperature heat pipe, with a cooling or chilling means located near the junction of the two heat pipes. Means are provided for moving the two heat pipes together along the longitudinal axis so that the mold effectively moves out of the hotter heat pipe and into the cooler one.
Because the heat pipes are substantially isothermal along their lengths, each with different temperature, the temperature gradient at their junction is rather steep and approaches a step function. The thermal gradient is considerably sharper than that produced by conventional means.